1. Field of the Invention
The present invention relates to an articulated robot and, more particularly, to an articulated robot for carrying a substrate, such as a semiconductor wafer.
2. Description of the Related Art
FIG. 15 shows a prior art articulated robot 1 disclosed in JP-A No. 2001-137181 in a plan view. The articulated robot 1 is used for carrying a semiconductor wafer 2. The articulated robot 1 has a first arm 3, a second arm 4, a third arm 5, a hand unit 6 for holding the wafer 2, and a base 7. The articulated robot 1 moves the hand unit 6 holding the semiconductor wafer 2 in predetermined first directions X along a straight path. The first arm 3 has a base part 3a pivotally supported on the base 7, and a front part 3b. The second arm 4 has a base part 4a and a front part 4b, the third arm 5 has a base part 5a and a front part 5b, and the hand unit 6 has a base part 6a. The front part 3b of the first arm 3 and the base part 4a of the second arm 4 are pivotally connected together. The front part 4b of the second arm 4 and the base part 5a of the third arm 5 are pivotally connected together. The front part 5b of the third arm 5 and the base part 6a of the hand unit 6 are pivotally connected together.
The base 7 has a first axis L1 and the first arm 3 turns about the first axis L1. The first arm 3 has a second axis L2 and the second arm 4 turns about the second axis L2. The second arm 4 has a third axis L3 and the third arm 5 turns about the third axis L3. The third arm 5 has a fourth axis L4 and the hand unit 6 turns about the fourth axis L4. The distance N1 between the first axis L1 and the second axis L2, the distance N2 between the second axis L2 and the third axis L3 and the distance N3 between the third axis L3 and the fourth axis L4 are in the ratio of 2:2:1.
When the hand unit 6 moves straight in the first direction X, a middle point 8 of the second arm 4 moves along a reference line 9 perpendicularly intersecting the first axis L1; that is, the respective angular speeds of the first arm 3, the second arm 4, the third arm 5 and the hand unit 6 are in the ratio of 1:2: 2:1.
FIG. 16 shows an articulated robot 1 in a first modification of the articulated robot 1 shown in FIG. 15. Referring to FIG. 16, a first arm 3, a second arm 4 and a third arm 5 extend straight along a reference line 9 parallel to first directions when a hand unit 6 is moved to a position farthest from a base 7. When a wafer 2 held by the hand unit 2 is moved in the first direction X toward or away from the base 7, a first joint 11 joining the first arm 3 and the second arm 4 move in a second direction Y1 with respect to the base 7, while a second joint 12 joining the second arm 4 and the third arm 5 moves in a second direction Y2 opposite the second direction Y1. When a third joint 13 joining the hand unit 6 and the third arm 5 is moved toward the base 7, the first joint 11 moves away from the reference line 9 in the second direction Y1, the second joint 12 moves away from the reference line 9 in the second direction Y2. In some cases, the distance B1 between the reference line 9 and the second joint 12 and the distance B2 between the reference line 9 and the first joint 11 are longer than the distance A1 between the reference line 9 and one end of a diameter of the wafer 2 and the distance A2 between the reference line 9 and the other end of the diameter as shown in FIGS. 16(2) to 16(4). In such cases, the articulated robot 1 needs an working area of a width in the second directions Y1 and Y2 greater than a width equal to the sum of the distances B1 and B2 in the opposite second directions Y1 and Y2 in which the first joint 11 and the second joint 12 move with respect to the reference line 9 in order that the first joint 11 and the second joint 12 may not interfere with other devices installed around the articulated robot 1 when the first joint 11 and the second joint 12 are moved in the second directions Y1 and Y2.
FIG. 17 shows an articulated robot 1 in a second modification of the prior art articulated robot 1 in a plan view. The articulated robot 1 can be changed from a left-hand system in which the first joint 11 is moved in the second direction Y1 to a right-hand system in which the first joint 11 is moved in the second direction Y2, and vice versa. As shown in FIG. 17(1), the articulated robot 1 cannot be changed from the right-hand system to the left-hand system in a state where the radius of turning circle having its center on a first axis L1 is a minimum.
Arms 3 to 5 extended in a state shown in FIG. 17(1) need to be extended in a line along a reference line 9 as shown in FIG. 17(2) when the articulated robot 1 is changed from the left-hand system to the right-hand system. Thus, an additional operation is needed to change the articulated robot 1 from the right-hand system to the left-hand system and hence the articulated robot 1 cannot be changed in a short time from the right-hand system to the left-hand system. The change of the articulated robot 1 from the left-hand system to the right-hand system needs a similar operation and has a similar problem.
In a state shown in FIG. 17(2) permitting changing the articulated robot 1 from the right-hand system to the left-hand system, the arms 3 to 5 are extended along the reference line 9 and the distance D along the first direction between a base 7 and a third joint 13 is greater than a minimum radius C of a turning circle. Therefore, the articulated robot 1 needs a working area greater than the distance D in the first direction between the base 7 and the third joint 13 around the articulated robot 1 in order to prevent the interference of the articulated robot 1 with devices installed around the articulated robot 1 in changing the articulated robot 1 between the right-hand system and the left-hand system.
Thus, the known articulated robot 1 needs a large working area. When the articulated robot 1 is used in a housing through which clean air flows, the housing must be large and the efficiency of cleaning the interior of the housing with clean air is low. The ratio of the working area of the articulated robot 1 to an internal space in the housing is large and only a small space is available for installing other processing devices in the housing.